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R2/C2 Linear Rail Bracket Ends

Discussion in 'Projects' started by WheresWaldo, Sep 30, 2017.

  1. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    I am requesting some community help here. I reverse engineered the split bracket ends that hold the double 6 mm linear rails. The R2 uses what I believe is a 600 mm closed loop GT2 belt, but other than a spring that puts a king in the belt to tighten it, there is no real adjustment to tighten the belt at all. Someone with a C2 should be able to check the length of the corresponding closed loop GT2 belt. You also cant use a straight belt as there is no way to secure the ends. I made the model in Fusion 360 and am sharing it here in the hope that someone much smarter than me can add a mechanism in the tiny space provided that can allow for a standard belt (open not closed) or at the very least a way to increase the belt tension.

    Advantages to using an open belt would be things such as availability of fiberglass or steel cores. Ability to buy a long length of GT2 belt so as to have convenient spares. Adding an adjuster to the existing belt system would allow better tension control and perhaps a bit less backlash.

    It takes three screws to hold it together and is sized for thread-forming screws for thin plastic in a M2.5 x 12 mm size. Without recesses for the head you can insert the screws from either side. Both halves of the shell are currently identical.

    The model is located here at the following link and may be downloaded in a number of 3D model formats or as a mesh file (STL) for simply printing.

    R2-C2 Screw Together Brackets v4.png
     
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  2. Ed Ferguson

    Ed Ferguson Active Member

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    Nice job on the modeling. I downloaded the file in case I have a need someday.

    I suggest modifying to use brass heat-set inserts to allow 4-40 machine screws rather than thread-forming screws. I'm a big fan of using these inserts on everything I print that is made for dis-assembly. You would need to increase the diameter of the bosses to handle the heat for 3 seconds. That may require moving the third screw hole so it sets a bit more between the pair of smaller rails. It would take a thin jewelers screwdriver to go between the rails however.

    As far as belt tension, obviously not much room to play with there. Have to think about it :)

    4-40 insert.jpg
     
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  3. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    I figured doing it with screws makes it serviceable rather than the snap fit that Robo uses. Two snaps and a tab is broken, two more and now you have to zip tie or glue the halves together. The reason I didn't use the heat set inserts is that 3 mm is too big and because of what you mentioned about having to make them more beefy. The posts are exactly in the spot that Robo put their's, but I wanted /hoped people would play with them and move stuff around, that is why I make it completely open and downloadable.

    Where the top post is located Robo has a belt tension sprint that goes around it that is why they placed it there. I think it could easily be relocated if need be.

    DSC_8116a_grande[1].jpg
     
    #3 WheresWaldo, Sep 30, 2017
    Last edited: Sep 30, 2017
  4. Ed Ferguson

    Ed Ferguson Active Member

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    Here's a configuration I came up with based on your model.

    Screw hole bosses relocated and enlarged to 8mm OD to handle heat while installing brass 4-40 heat-set inserts.

    Belt clamped in serrated section of bracket. Belt tension adjusted by re-positioning belt (cutting first if necessary) along the clamp.

    Several belt joiners on Thingiverse use this method, so I assume it works well.
    https://www.thingiverse.com/thing:2521953
    https://www.thingiverse.com/thing:1470667
    https://www.thingiverse.com/thing:627214

    If the belt clamp is too tight, perhaps the outer ends could be made to float freely rather than be connected to the outer walls (perhaps by making the belt clamp a separate piece that drops into the bracket). This way there may be enough "spring" to allow the belt to slide in easier.

    Another idea is to extend the belt clamp upward to the full width of the belt on one-half of the bracket, and leave the other half empty. This would mean the two bracket halves are not interchangeable, but it may be easier to get the belt on & adjusted before securing the mating half of the bracket.

    R2 Bracket with Clamp.jpg
     
    #4 Ed Ferguson, Sep 30, 2017
    Last edited: Sep 30, 2017
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  5. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    What if the belt connector was a separate piece that just fit in place between the two shells.

    The only reason I modeled it symetrical is that I was going to duplicate the clips and then decided not to.
     
  6. Ed Ferguson

    Ed Ferguson Active Member

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    Should work. As long as it's a tight fit so there is no shifting as the belt changes direction.
     
  7. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    @Ed Ferguson 38 mm is the exact dimension. What CAD program are you using?
     
    #7 WheresWaldo, Sep 30, 2017
    Last edited: Oct 1, 2017
  8. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    How about this one, http://a360.co/2yBTmFT

    It uses 2.0 mm heat set inserts and M2 x 12 mm Stainless Steel socket head screws that are recessed in the body. Design can be downloaded from the link above.

    R2_C2 Linear Rail Brackets.png

    These are the two McMaster-Carr part numbers:

    91292A834 - screws
    94180A307 - inserts​
     
    #8 WheresWaldo, Oct 1, 2017
    Last edited: Oct 1, 2017
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  9. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Changed a few things around, now to print it out and test. Same link as previous iteration listed in the message above.
     
    #9 WheresWaldo, Oct 1, 2017
    Last edited: Oct 1, 2017
  10. Ed Ferguson

    Ed Ferguson Active Member

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    Looks like it should work. Curious to see photos when partially assembled.
     
  11. adikted2astro

    adikted2astro Active Member

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    I'm extremely interested in these. I bought some 8mm ID plug graphite bushings and was going to install them today along with other stuff, but it took me almost 30 minutes to get ONE of the original brackets off! Ridiculous.........I do not like them. Having brackets like these would be way easier to disassemble and I'm a huge fan of socket head cap screws. Post pics when you have something. I'd really like to do this if it works well.
     
  12. crussty

    crussty Moderator

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    Above my ability to CAD, but what about something along the lines of a tin-can key to tension the belts? The "key" part would be removed, but the slotted tensioner would stay internal.
     

    Attached Files:

  13. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    @crussty How would you propose to use that part. The belts are endless (loops) and the gantry is designed to take a very specific size loop, there should be no need to tension beyond the simple spring that sits inside the bracket. I believe this is a copy of how Ultimaker does their gantry belts and you rarely hear of any issues with those.
     
  14. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Those belts are not under any significant stress and should not stretch enough to really matter. I have seen nothing like that so far :)
     
  15. Geof

    Geof Volunteer Moderator
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    almost an exact copy. Have mine tore apart waiting on parts, will try to snap some pics of their set up for fun.
     
  16. crussty

    crussty Moderator

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    Sorry, it was my misunderstanding. I thought the end goal was to use cut belt rather than the closed loop.
     
  17. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    @crussty there should be no need to cut the belts, the gantry is designed to take either a 606 mm or 610 mm closed loop belt, I don't remember which. There is no need to over-tension the belts, it isn't a smooth belt like used in most motor vehicles.
     
  18. albert3d

    albert3d Member

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    Just found this. Great job @WheresWaldo! Anyone print either version and try it? I haven't opened mine up yet to see what is inside, but is it a self lube bronze bushing sleeve? If so, why does Robo have us putting lube on those outside rails? I can see for the extruder bearings, but I thought the bronze bushings didn't need it. Anyone have a link for replacement bearings that will fit in these? I wish Robo would release all the files for the plastic parts on these machines.
     
  19. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Not since the Beta has Robo done this. Even the R1 was done by a member (who released CAD versions of everything).
    @Mike Kelly did an awesome job -- I still use that information to this day.
     
  20. albert3d

    albert3d Member

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    I think their lack of being truly open source is a downfall. Even though I have heard the words out of Braydon's mouth on interviews that the R2/C2 are fully open source. But I'll digress before the hairs on my neck start to stand up.
     

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